The invention described herein relates to refueling machines for a nuclear reactor and more particularly to an improved machine incorporating features designed to increase its reliability and to perform the refueling operation in a more efficient and economical manner.
During the operating life of a nuclear reactor, at periodic intervals, a portion of the reactor fuel assemblies are completely removed from the reactor core and disposed of as spent fuel. These assemblies are replaced by fresh assemblies, while the other fuel assemblies remaining in the core are shifted to different positions to achieve maximum power output with optimum utilization of energy contained in the nuclear fuel. As refueling takes place, each fuel assembly must remain completely submerged in neutron absorbing coolant to prevent fissioning and consequent generation of heat in the fuel rods.
To facilitate the refueling process, different designs of refueling apparatus have heretofore been used which incorporate features designed to achieve apparatus reliability, safety and economy in manufacture. One well known design in U.S. Pat. No. 4,086,132 assigned to the same assignee as the present invention, includes provision for removing control rod thimble plugs from the top of certain fuel assemblies, together with features for separately lifting a fuel assembly from the core. This patented design utilizes a housing which encloses a vertically movable mast arranged to actuate fingers into locking engagement with a fuel assembly, and provides for interlocks designed to positively hold the fuel assembly during transfer from the reactor core to a spent fuel cell. The refueling machine is efficient and reliable but because the equipment is designed to serve two functions, i.e., to remove a complete assembly and/or in a separate action, to remove the thimble plugs from the assembly, machine construction costs are high although maintenance cost appear to be minimal. Also, since operators cannot directly observe the refueling machine operation when the gripper portion of the machine and the fuel assembly is submerged, greater simplicity in design desirably should be incorporated in the refueling apparatus.